Transistors on two-dimensional semiconductors: contact resistance limited by the contact edges

Arutchelvan, Goutham; Matagne, P.; Rosa, C. Lockhart de la; Sutar, Surajit; Gendt, Stefan De; Heyns, Marc; Radu, Iuliana

doi:10.1109/iitc-amc.2017.7968951

Cited by 7 publications

(11 citation statements)

References 6 publications

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“…3a shows that Ion (@ ns = 10 13 cm -2 ) does not degrade as Lcont is scaled down to 13nm. This agrees with TCAD simulations 10,17,18 that predict contact edge injection of carriers for 1-3 layers of MoS2 channel. This observation holds true for three different Lch (30 nm, 100 nm, nm) over a wide range of Lcont (500nm to 13nm) and for varying lateral field (VDS = 0.05 V, V).…”

Section: B Contact Length Scalingsupporting

confidence: 87%

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

Arutchelvan¹,

Smets²,

Verreck³

et al. 2021

Preprint

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Two-dimensional semiconducting materials are considered as ideal candidates for ultimate device scaling. However, a systematic study on the performance and variability impact of scaling the different device dimensions is still lacking. Here we investigate the scaling behavior across 1300 devices fabricated on large-area grown MoS2 material with channel length down to 30 nm, contact length down to 13 nm and capacitive effective oxide thickness (CET) down to 1.9 nm. These devices show best-in-class performance with transconductance of 185 μS/μm and a minimum subthreshold swing (SS) of 86 mV/dec. We find that scaling the top-contact length has no impact on the contact resistance and electrostatics of three monolayers MoS2 transistors, because edge injection is dominant. Further, we identify that SS degradation occurs at short channel length and can be mitigated by reducing the CET and lowering the Schottky barrier height. Finally, using a power performance area (PPA) analysis, we present a roadmap of material improvements to make 2D devices competitive with Silicon gate-all-around devices.

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Section: B Contact Length Scalingsupporting

confidence: 87%

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

Arutchelvan¹,

Smets²,

Verreck³

et al. 2021

Preprint

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“…To verify such prediction, τ RC is calculated as τ RC = R L × C , where R L is the load resistance and C is junction capacitances of p-i-n diode. We use the following formula, to calculate the value of C , where ε is the in-plane dielectric constant (8.5), k is the electrostatic force constant (8.99 × 10 9 N·m 2 /C 2 ), W and L represent the width and length of WSe 2 channel, respectively. C is calculated to be about 6 × 10 –6 pF.…”

Section: Resultsmentioning

confidence: 99%

An Ultrafast WSe₂ Photodiode Based on a Lateral p-i-n Homojunction

et al. 2021

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High-quality homogeneous junctions are of great significance for developing transition metal dichalcogenides (TMDs) based electronic and optoelectronic devices. Here, we demonstrate a lateral p-type/intrinsic/n-type (p-i-n) homojunction based multilayer WSe2 diode. The photodiode is formed through selective doping, more specifically by utilizing self-aligning surface plasma treatment at the contact regions, while keeping the WSe2 channel intrinsic. Electrical measurements of such a diode reveal an ideal rectifying behavior with a current on/off ratio as high as 1.2 × 106 and an ideality factor of 1.14. While operating in the photovoltaic mode, the diode presents an excellent photodetecting performance under 450 nm light illumination, including an open-circuit voltage of 340 mV, a responsivity of 0.1 A W–1, and a specific detectivity of 2.2 × 1013 Jones. Furthermore, benefiting from the lateral p-i-n configuration, the slow photoresponse dynamics including the photocarrier diffusion in undepleted regions and photocarrier trapping/detrapping due to dopants or doping process induced defect states are significantly suppressed. Consequently, a record-breaking response time of 264 ns and a 3 dB bandwidth of 1.9 MHz are realized, compared with the previously reported TMDs based photodetectors. The above-mentioned desirable properties, together with CMOS compatible processes, make this WSe2 p-i-n junction diode promising for future applications in self-powered high-frequency weak signal photodetection.

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“…However, the doping still improves the contact resistance by thinning the SB even though it cannot affect the metal−semiconductor interface under the contacts. 32,42,66,67 This apparent contradiction can be explained by a two-path current injection model at the contacts, which is essential to understanding SCTD. 66−68 One path injects carriers vertically from the metal to the semiconductor under the contact, which is therefore largely unaffected by the channel doping.…”

mentioning

confidence: 99%

“…This second path can comprise a significant or even dominant portion of the total carrier injection for thin semiconductor channels. 66,67 It is this mechanism that produces the contact resistance and doping response seen in devices with no doping in the contact regions.…”

mentioning

confidence: 99%

“…It should also be noted that most SCTD investigations in the literature dope the channel after the contacts have been fabricated, producing no charge under the contacts. However, the doping still improves the contact resistance by thinning the SB even though it cannot affect the metal–semiconductor interface under the contacts. ,,, This apparent contradiction can be explained by a two-path current injection model at the contacts, which is essential to understanding SCTD. − One path injects carriers vertically from the metal to the semiconductor under the contact, which is therefore largely unaffected by the channel doping. However, the second 1D path injects carriers directly from the corner of the contact into the top portion of the channel, which is immediately adjacent to the doping charge.…”

mentioning

confidence: 99%

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Thickness Trends of Electron and Hole Conduction and Contact Carrier Injection in Surface Charge Transfer Doped 2D Field Effect Transistors

2020

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One of the main limiting factors in the performance of devices based on two-dimensional (2D) materials is Fermi level pinning at the contacts, which creates Schottky barriers (SBs) that increase contact resistance and, for most transition metal dichalcogenides (TMDs), limit hole conduction. A promising method to mitigate these problems is surface charge transfer doping (SCTD), which places fixed charge at the surface of the material and thins the SBs by locally shifting the energy bands. We use a mild O 2 plasma to convert the top few layers of a given TMD into a substoichiometric oxide that serves as a p-type SCTD layer. A comprehensive experimental study, backed by TCAD simulations, involving MoS 2 , MoSe 2 , MoTe 2 , WS 2 , and WSe 2 flakes of various thicknesses exposed to different plasma times is used to investigate the underlying mechanisms responsible for SCTD. The surface charge at the top of the channel and the gate-modulated surface potential at the bottom are found to have competing effects on the channel potential, which results in a decrease in the dopinginduced threshold shift and an increase in minimum OFF state current with increasing thickness. Additionally, an undoped channel region is shown to mitigate carrier injection issues in sufficiently thin flakes. Notably, the band movements underlying the SCTD effects are independent of the particular semiconductor material, SCTD strategy, and doping polarity. Consequently, our findings provide critical insights for the design of high-performance transistors for a wide range of materials and SCTD mechanisms including TMD devices with strong hole conduction.

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Transistors on two-dimensional semiconductors: contact resistance limited by the contact edges

Cited by 7 publications

References 6 publications

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

An Ultrafast WSe₂ Photodiode Based on a Lateral p-i-n Homojunction

Thickness Trends of Electron and Hole Conduction and Contact Carrier Injection in Surface Charge Transfer Doped 2D Field Effect Transistors

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Transistors on two-dimensional semiconductors: contact resistance limited by the contact edges

Cited by 7 publications

References 6 publications

Impact of Device Scaling on the Electrical Properties of MoS2&nbsp;Field-effect Transistors

Impact of Device Scaling on the Electrical Properties of MoS2&nbsp;Field-effect Transistors

An Ultrafast WSe2 Photodiode Based on a Lateral p-i-n Homojunction

Thickness Trends of Electron and Hole Conduction and Contact Carrier Injection in Surface Charge Transfer Doped 2D Field Effect Transistors

Contact Info

Product

Resources

About

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

Impact of Device Scaling on the Electrical Properties of MoS2 Field-effect Transistors

An Ultrafast WSe₂ Photodiode Based on a Lateral p-i-n Homojunction